Hi!
The app for FIrefox OS in the Marketplace is only available for Firefox OS devices. I have done some tests and it works also on Tablet, Firefox for Android and Desktop, so I would suggest to edit the listing and add those devices too.
And well, the app is not available for China, I bet that they would like to use it too
Finally, the Nginx server is providing the manifest with the content-type āapplication/octet-streamā, but the type should be āapplication/x-web-app-manifest+jsonā. That is a nasty error that should be fixed ASAP or the Marketplace could reject the app from the Marketplace.
Best regards.